The invention relates broadly to immobilization and release of active material within hydrogel microbeads. The hydrogel microbeads can be used to immobilize water soluble and water insoluble actives such as oils, fragrances, lubricants, and agricultural chemicals such as pheromones, herbicides, insecticides and pesticides.
Methods of eliminating unwanted pests from orchards, crops and forests frequently entail the use of organophosphate insecticides. Alternative methods involve insect mating disruption, where insect pheromones are used to control pests and protect agricultural crops. In insect mating disruption methods, the mating pheromone plume of a female insect is typically masked with other pheromone point sources. This reduces the likelihood of a male insect finding a female, and subsequently disrupts and reduces larvae production. The insect population of the next generation is thus decreased, as well as potential crop damage.
Conventional sprayable pheromone formulations are generally provided in liquid filled microcapsules containing an active. Typically, the microcapsules have a polyurea membrane that can be formed using an interfacial process involving an isocyanate and an amine. Microencapsulation by this method has been descibed for example in U.S. Pat. No. 4,487,759 (Nesbitt et al., 1984). These polyurea membranes allow actives to be released into the atmosphere for up to a total of 2-3 weeks for most insect pheromones.
Use of interfacial condensation to encapsulate substances such as pharmaceuticals, pesticides and herbicides is taught in U.S. Pat. No. 3,577,515. The encapsulation process involves two immiscible liquid phases (typically water and an organic solvent), one being dispersed in the other by agitation, and the subsequent polymerization of monomers from each phase at the interface between the bulk (continuous) phase, and the dispersed droplets. Polyurethanes and polyureas are materials suitable for producing the microcapsules. The microcapsules comprise a polymeric sphere and a liquid center, ranging from 30 micron to 2 mm in diameter, depending on monomers and solvents used.
Highly viscous and thickened hydrogels have been used to deliver pheromones, fragrances and other non-water soluble actives. U.S. Pat. No. 4,755,377, for example, describes a process of encapsulating perfume or fragrant material within an aqueous-based gel composition. The resulting material is in the form of a highly viscous semi-solid. U.S. Pat. No. 5,645,844 describes the use of chitosan paste for delivery of pheromones to disrupt insect mating, where the material can be dispensed by an apparatus such as a caulking gun. Due to their thickness and high viscosity, these materials, however, are generally unsprayable compositions.
Most hydrogels are safe and non-toxic to humans. Hydrogels have been used for encapsulation of biological materials whereby the formulation is non-lethal to the viability of cells, proteins, and related materials. U.S. Pat. No. 4,689,293, describes the process of encapsulating living tissue or cells in alginate beads. The encapsulation shell permits the passage of materials and oxygen to the cells and permits the diffusion of the metabolic by-products from the gel.
A method of delivering active material using a plurality of microbeads suspended in solution is provided, where the microbeads comprise a hydrophilic matrix having droplets of active material entrained therein. Furthermore, the matrix is capable of immobilizing a broad spectrum of active materials, either water soluble or non-water soluble. In one aspect of the invention, the hydrophilic matrix may be made from a naturally occurring material to provide an environmentally friendly microbead.
In another aspect of the invention, the active entrained in the matrix diffuses from the hydrophilic matrix and is released into the environment over an extended period.
In yet another aspect, the microbeads are capable of re-hydrating after an initial dehydration and release of active. Thus, the release and longevity of the active can be controlled by adjusting the humidity of the environment in which the microbeads have been delivered.